I. Field of the Invention
The present invention relates to an apparatus for detecting increases in heat, particularly for detecting dangerous increases in heat caused by conditions such as by fire, spontaneous combustion, or the like, in a high-voltage environment such as an electrostatic spray paint system.
II. Description of the Prior Art
Typical apparatus for detecting increases in heat such as would indicate a fire, spontaneous combustion, or a like condition are employed in fire suppression systems to suppress the condition causing the increased heat. For example, in an electrostatic spray paint environment, it is sometimes possible for the paint in the painting area, or booth, to catch fire or to spontaneously combust. In that event, it is necessary to suppress the condition by immediately expelling a fire suppressing material into the zone of increased heat. Typical suppressing materials would be Halon 1301, dry chemical, carbon dioxide, and foam.
With particular reference to electrostatic spray paint systems, there is a recognized risk of fire, especially in the vicinity of the spray paint nozzle from which the paint is emitted. In such systems, the nozzles are raised in potential to several thousands of volts. As a result, the paint which is emitted from the nozzles is thus highly charged. Because of the high charge concentrations and large voltages involved, the use of electrically conducting heat detectors in the vicinity of the nozzle has been avoided. Accordingly, either nonelectrically conductive heat detectors have been employed near the nozzle, and/or electrically conductive detectors have been utilized at a location remote from the nozzle. Such previous heat detectors suffered several drawbacks.
One such detector employs an infrared detector coupled to an electronic circuit which circuit controls expulsion of the fire suppressing materials. The detector would typically be placed above the area of active spray painting and the detector's line of sight directed toward the center of that spraying area. In the event of a fire, for example, the amount of infrared light sensed by the detector would increase. The electronic circuit detects the increase and if the increase is sufficiently large to indicate a dangerous condition, the electronic circuit would initiate fire suppression techniques such as the expelling of the suppressing materials. One drawback to such a detector is that it is remote from the nozzle and hence may not detect a dangerous increase in heat at the nozzle sufficiently quick to permit suppression of the condition before damage to the equipment or risk to humans is unavoidable. Further, such a detector is too bulky to be placed near the nozzle. Moreover, even if such placement were easily accomplished, the field of view or line of sight, of the detector is too limited. Hence, a dangerous increased heat condition could go undetected for too long a period of time. An additional drawback of such a system is that it is subject to the effects of ambient light. For example, some portions of the electrostatic spray paint systems may be contained within a dark booth or cabinet. Entering the booth for servicing or any other reason will require opening an accessway which will likely permit light to enter. In response to the light, the electronic circuit will undesirably initiate the fire suppression techniques.
An alternative type of heat detector utilizes a pressurized hose or tube. For example, a length of nylon or vinyl hose is pressurized with nitrogen. In the event that the heat increase is sufficient to melt or otherwise break down the hose material, the nitrogen within the hose will escape causing a sudden drop in pressure. The drop in pressure may act to mechanically release or open a valve thereby actuating the fire suppression techniques. Alternatively, a transducer situated in a circuit including the pressurized line and coupled to the electronic circuit could sense the drop in pressure. The electronic circuit which is responsive to the transducer initiates the above fire suppression techniques. The pressurized hose approach may be employed to detect increased heat conditions near the nozzle as the pressurized hose comprises an electrically non-conductive detector.
The use of pressurized hose also has drawbacks, however. One problem with the pressurized hose approach is that the system is prone to air leaks which look to the electronic circuit as through it were a dangerously-increased heat condition. There are also additional drawbacks in specific applications For example, there is a strong move in the electrostatic spray paint industry towards robotics. A robotically-controlled arm carries paint lines to a spray paint nozzle which is movably supported at the free end of the arm. The nozzle and arm may move in a variety of directions to permit complete paint coverage of the object to be painted. Due to the wide variety of movements possible, a large volume of space must be monitored for fire and the like. To provide adequate detection over the entire vicinity of interest, it is necessary that a portion of the pressurized hose be attached to the structure of the robot arm as well as having a portion spaced adjacent the spray paint nozzle so as to ensure that the detector is always located near the most likely sources of fire. In such a system, the air leak problem with pressurized hose is aggravated. Specifically, the diversity of movements of the arm and the nozzle may tend to induce leaks in the pressurized hose. Additionally, certain space constraints imposed in a robotic system may be too severe to permit use of pressurized hose. Typical pressurized hose is at least 1/4 inch in diameter and in the robot arm environment, there may not be sufficient space to accommodate the hose.